The ammonia chemical ionization (NH3/CI) spectra of phenylpropanoids and substituted phenylalkyl phenyl ethers containing a-hydroxy or a-carbonyl functional groups are discussed. Fragmentation reactions which occur in the temperature range 180-450 °C are examined to model pyrolysis mass spectrometric experiments of lignin. Hydroxycinnamyl alcohols and a-hydroxy phenylalkyl phenyl ethers show abundant [M + H — H2O]+ elimination ions and to a lesser extent [M + NH4 — H2O]+ substitution ions while hydroxycinnamic acids and a-carbonyl phenylalkyl phenyl ethers show predominantly [M + H]+ and [M + NH4]+ ions. The interpretation of functional group information is facilitated by using trideuterioammonia (ND3) and [15N]ammonia (15NH3) as reagent gases. Labile hydrogens undergo essentially complete exchange upon ND3/CI and the number of hydroxyl functional groups is readily determined by comparison of the [M + NH4]+ and [M—nH+nD+ND4]+ adduct ions. Incomplete H-D exchange is observed for enolizable and aromatic protons.

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Journal J. Mass Spectrom.
Citation
van der Hage, E. R. E, Weeding, T. L, & Boon, J. J. (1995). Ammonia chemical ionization mass spectrometry of substituted phenylpropanoids and phenylalkyl phenyl ethers. J. Mass Spectrom., 30, 541–548.